A glow plug is used to aid starting a diesel engine. The glow plug is configured to include a heater having, for example, a resistor having a folded shape, a pair of leads joined to each end of the resistor, and an insulating base in which the resistor is buried at the front side thereof and the pair of leads are buried at the rear side thereof. The glow plug of such configuration has been desired to have higher temperature performance and higher durability because the glow plug is also used to provide after glow for exhaust gas purification, for example, in order to comply with higher environmental standards.
In order to satisfy such requirements, a ceramic grow plug which can be used at higher temperature has been used. However, microcracks or the like due to resistance changes or thermal expansion differences tend to occur at junctions between the resistor and the leads, and resistance changes and dielectric breakdown (short-circuit) between the leads caused by the microcracks or the like have posed problems.
Then, the problems are, for example, addressed by configuring a joint surface of the resistor and the lead where microcracks are likely to occur to incline as viewed in cross section parallel to the axis of the leads and increase the durability by increasing the area of the joint surface (PTLs 1 and 2).